A set of straight and gleaming teeth makes for a beautiful smile. But how many people who have had a little dental work know that inside their mouths may be some of the first products of a new industrial revolution?

Tens of millions of dental crowns, bridges and orthodontic braces have now been produced with the help of additive manufacturing, popularly known as 3-D printing. Industrial 3-D printers, which can cost up to $1 million, are changing manufacturing.

The business of dentures shows how. For the metal bits in false teeth, dentists have long relied on a process called “investment casting.” It is fiddly, labor-intensive and not always accurate; then again the method is some 5,000 years old.

Things are done differently at a plant in Miskin, Wales, set up by Renishaw, a British engineering company. The plant has three of the firm’s 3-D printers; more will be added soon. Each produces a batch of more than 200 dental crowns and bridges from digital scans of patients’ teeth. The machines use a laser to steadily melt successive layers of a cobalt-chrome alloy powder into the required shapes. The process can take eight to 10 hours, but the printers run unattended and make each tooth to a design unique to every patient. Once complete, the parts are shipped to dental laboratories all over Europe where craftsmen add a layer of porcelain.

The mouth isn’t the only bodily testing ground for 3-D-printed products. Figures gleaned by Tim Caffrey of Wohlers Associates, a U.S. consultancy, show that more than 60 million custom-shaped hearing-aid shells and ear molds have been made with 3-D printers since 2000. Hundreds of thousands of people have been fitted with 3-D-printed orthopedic implants, from hip-replacement joints to titanium jawbones, as well as various prosthetics. An untold number have benefited from more accurate surgery done using 3-D-printed surgical guides; about 100,000 knee replacements are performed this way every year. Compared with the $70 billion machine-tool market, additive manufacturing is still tiny. But it is growing rapidly, and not just in health care. Overall, Wohlers estimates that 3-D-printed products and services grew 26 percent last year, to be worth nearly $5.2 billion. McKinsey, a consultancy, reckons that in terms of things like better products, lower prices and improved health, 3-D printing could have an economic impact of up to $550 billion a year by 2025.

A Minnesota influence

One reason 3-D printers are becoming more mainstream is that the “inks” they use are getting better thanks to advances in materials science, says Andy Middleton, the European head of Stratasys, an Eden Prairie company that makes 3-D printers.

One method Stratasys uses, called PolyJet, is similar to inkjet printing: cartridges deposit layers of a liquid polymer that are cured with ultraviolet light. The company has just unveiled a new model called the J750. It uses multiple cartridges to print items in 360,000 colors and any combination of six materials, which can be rigid or flexible, opaque or transparent.

The machine is intended to make prototypes, as the polymers are not yet robust enough for a final product. Still, the ability to make realistic prototypes greatly speeds up product approval and the time it takes to get to market.

Increasingly, however, 3-D-printed objects are being produced as finished items. This leads consultants at PWC to conclude that additive manufacturing “is crossing from a period of hype and experimentation into one of rapid maturation.” They found more than two-thirds of U.S. manufacturers are now using 3-D printing in some form.

Another 3-D-printing process used by Stratasys builds parts layer by layer, by heating and extruding thermoplastic filaments. Airbus now uses these machines to print internal cabin fittings for its new A350 XWB airliner.

While further development is needed, the technology is already trusted enough to be used in products that must withstand high stresses and strains. GE has spent $50 million installing a 3-D printing facility at a plant in Auburn, Ala., to print up to 40,000 fuel nozzles a year for the new LEAP jet engine it is making with Snecma, a French firm. The finished item will be 25 percent lighter and five times more durable than a fuel nozzle made with conventional processes.

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